Precursor chemicals for semiconductor manufacturing process must be purified to meet the needs for depositing high quality films. Moisture and organic species are the impurities commonly found in the precursor chemicals. The traditional distillation can separate the impurities from the precursor chemicals. However, this method is too expensive and requires a sophisticated system. In addition, some of the precursor chemicals may be heat sensitive and decompose at high temperature so that the distillation method is limited in the application. Another traditional method is to use adsorbents to remove trace impurities in the precursor chemicals. Tests have found that some of the precursor chemicals are not compatible with adsorbents including activated carbons, molecular sieves, and other synthetic adsorbents. For example, dimethyldimethoxysilane as a low-k precursor exhibits some decomposition after contacting with the mentioned adsorbents, resulting in the formation of impurities.
U.S. Pat. No. 6,878,657 discloses the use of liquid phase alkoxide to deposit on the surface of zeolite NaA to change the pore size for selectivity. This method is useful to modify the specific adsorbent for more precise mouth opening of the pores and, therefore, gas species having close sizes would be separated. However, the surface modified zeolite still does not address decomposition of the precursor materials because the precursor materials may still decompose after contact with the adsorbent.
U.S. Pat. No. 6,890,373 discloses a method to prepare adsorbent that will not shed particles under pressure. The adsorbent was prepared by depositing metal compound and water soluble polymer on a core particle of adsorbing material and then coating it with polymer material. This type of adsorbent has the potential of preventing the direct contact of adsorbing materials with the fluid to be purified. It also potentially increases the transport distance of impurities from the fluid into adsorbing material. It, too, does not address decomposition of organosilicon precursors due to the contact of organosilicon precursors and adsorbent.
U.S. Published Patent Application 2004/0038803 discloses a method to treat adsorbents by heating them to different temperatures under an inert gas purge, and then passivating the adsorbents by flowing corrosive gas through the adsorbent.
Others have proposed some solutions, including U.S. Pat. Nos. 6,852,299, 6,939,527, 6,797,036, and 6,892,473.